Botez, in U.S. Pat. No. 4,215,319, incorporated herein by reference, has disclosed a semiconductor laser which comprises a body of semiconductor material with a pair of spaced, substantially parallel grooves in a surface thereof with a land between the grooves. A first confinement layer overlies the surface of the substrate and the surfaces of the grooves, an active layer overlies the first confinement layer and a second confinement layer overlies the active layer. The active layer has a uniform thickness over the land and tapers in thickness in the lateral direction, i.e. the direction in the plane of the surface of the substrate and perpendicular to the axis of the grooves. The active layer is the recombination region of the laser with the light beam being generated and propagating in the portion of the active layer over the land. Botez, in U.S. patent application Ser. No. 251,651, U.S. Pat. No. 4,347,486, which is incorporated herein by reference, has disclosed a semiconductor laser which comprises the laser described above having a guide layer interposed between the first confinement layer and the active layer. The guide layer has an index of refraction less than that of the active layer but greater than that of either the first or second confinement layers so that a light beam generated in the active region propagates both in the thin active region and the relatively thicker guide layer, thereby forming a lasing mode having a significantly larger cross-sectional area.
Both of these lasers emit light in the lowest order lateral mode over ranges of output powers which depend on the particular laser type. Above these ranges of powers the gain and confinement of the higher order lateral modes are such that the lasers begin to emit light in these higher order lateral modes. It would be desirable to increase the discrimination against the higher order lateral modes, thereby increasing the range of output powers for which both lasers emit in only the lowest order lateral mode.